During endoscopic surgical procedures, a surgical site such as a knee joint, shoulder joint or other cavity in the body of a human or animal is viewed with an endoscope. Further in this patent application, the surgical site for an endoscopic procedure is referred to as the body cavity. The body cavity is irrigated with a clear liquid by means of a pump. This pump is further in this patent application referred to as an inflow liquid pump. The clear liquid is as a rule saline, and the pump is usually a peristaltic roller type pump.
Existing liquid management systems are either operated by a fixed flushing volume programmed by the operator of the system when starting the procedure (normally an ml/min value), or by a fixed pressure target for the system. This target pressure is selected by the operator of the system when starting the process. Existing pressure controlled systems have different ways of measuring the pressure, but the overall technique is to directly or indirectly measure the pressure on the irrigation side of the system. The limitation with the volumetric system is that an excessive liquid volume is needed to achieve a rinsing effect. The limitations with the fixed pressure target systems are firstly that it is impossible to flexibly change the pressure depending on the needs during the operation. Thereby an unnecessary high pressure is used in many cases resulting in tissue swelling and subsequently a risk of tissue damage. Secondly the fixed pressure controlled systems seldom operate at the fixed pressure target as the systems are based on the measurement of an indirect pressure in the operation site. When the operation site is drained of liquid it takes some time for such a system to react to a lower pressure due to volume/pressure hysteresis of the tissue, and the reaction time can sometimes be very long resulting in an unnecessarily long time of bad visibility during the endoscopic procedure.
With both the volumetric- and the fixed pressure target systems the body cavity expands as a result of the pressure from the irrigation, and the inside of the body cavity can be viewed with an endoscope. The pressure value of the saline solution is an important matter. The higher pressure, the better viewing of the area is accomplished. Also, the pressure holds back blood from vessels that are damaged as a normal effect of the surgical process. Emerging blood obstructs visibility, and it is of course in general desirable to stop bleeding during surgery. The pressure causes tension in the tissue. However, too high a pressure may cause tissue damage, which must be avoided as much as possible. Thus, a precise control of pressure in the body cavity is of vital importance. It is well known how to measure pressure in a liquid, but a direct measuring of pressure in the body cavity is not possible without introducing pressure measuring sensors together with the surgical instruments into the body cavity. However, this method is bulky, expensive and difficult to operate. Alternatively, body cavity pressure can be measured by making an extra perforation of the body for the introduction of a pressure-measuring sensor into the body cavity. The latter makes the surgical procedure more complex, and also causes inconvenience and risk to the patient.
Another problem with endoscopic procedures is that aforementioned blood in the body cavity reduces visibility. Also, the surgical procedures as a rule involve the removal of, or work on tissue, for instance the meniscus of the knee. This results in debris, namely particles of various sizes of tissue floating around in the liquid in the body cavity. This also reduces visibility for the surgeon. These difficulties are routinely managed by rinsing. To rinse out blood or debris, the liquid in the body cavity is replaced by introducing or increasing liquid flow through the body cavity. The pressure may optionally be temporarily elevated. This may stop bleeding as the pressure in the body cavity exceeds that of the blood pressure in the ruptured blood vessels in the body cavity. If the introduction of liquid is made with an inflow liquid pump, the operation is started by pressing a button, or by a foot-operated switch. However, if the outflow of liquid simultaneously is affected, introducing or increasing liquid outflow causes the pressure in the body cavity to drop. If the situation is severe, the flow necessary to rinse the body cavity may have to be very high, and this inevitably causes a significant drop in pressure, and could indirectly be dangerous to the patient as the surgeon is distracted. Furthermore, in some cases the pressure does in fact not drop as a rinse process is initiated. Instead, the body cavity is drained of liquid, but the pressure drops only insignificantly and a pressure regulation function does not foresee that the body cavity is drained. This is due to a high compliance of the body cavity, and in this example this may be the case if the body cavity is a shoulder or a urine bladder. The end result in this case is that the viewing area becomes too small for viewing with the endoscope, but the pressure nearly persists. These repeating obstructions of visibility can be disturbing for the surgeon, and also calls for some action from the user to change pressure, flow or the user may have to wait for quite some time for the situation to stabilize.
DE 3338758, GB 2260622 A, US 2003/0236488 A1, US 2004/0133149 A1, WO 86/00534 and EP 529902 all disclose a method to regulate pressure in an endoscopy system by means of a pressure transducer at the body cavity side of an inflow pump, and a regulating function of the inflow pump. All systems have in common the regulation of pressure of the inflow pump, as the generated pressure is measured by or near it.
In U.S. Pat. No. 5,520,638 a pressure measurement principle is disclosed, using an air filled bladder in the pressurized liquid. The pressurized air transfers the air pressure to a pressure transducer in the inflow pump system. The air filled bladder must be connected to a panel connector via an air line and connector. The major disadvantage of these solutions is that there is a risk of leakage in the air connection to the pump. Such leakage increases the pressure to levels that may endanger the patient, as pressure control is lost. Another disadvantage of these solutions is that the pressure by the pump is much higher than in the body cavity as a result of the resistance of flow in the irrigating system. The pressure generated by the inflow pump is controlled by measuring the pressure by the inflow pump itself. The control mechanism in the above mentioned references is a regulating function, where the generated pressure is measured via air filled tubing to a pressure transducer, or by measuring the pressure indirectly by detecting the small expansion of the tubing. The rotational speed of the inflow pump is set to maintain a preferred pressure.
In U.S. Pat. No. 5,556,378, a device is disclosed that measures the pressure difference between a pump irrigating a body cavity, and a suction pump removing liquid from the site. With this system it is complicated, however, to maintain a steady pressure in the body cavity, and two pressure measuring sensors and a complex system are necessary for a desired result. Also, control of flow is basically lost to achieve a desired pressure. This is highly undesirable, as flow should be under control during rinsing procedures, and minimized in between actions of rinsing.
In U.S. Pat. No. 4,998,914 a method to compensate for the conductance of the fluid line is disclosed. This is a way to measure pressure in the body cavity by an indirect method, but the method does not take flow changes into account. Thus, the pressure drop that occurs during a rinsing procedure is not compensated for.